Solution:

The root-mean-square (rms) voltage for a sinusoidal alternating voltage is given by $V_{rms} = \frac{V_0}{\sqrt{2}}$.
Rearranging for peak voltage $V_0$, we get $V_0 = \sqrt{2} V_{rms}$.
Hence, the peak voltage is $\sqrt{2}$ times the rms value of the ac source.